Simultaneous determination of three organophosphorus pesticides in different food commodities by gas chromatography with mass spectrometry

A sensitive and selective gas chromatography with mass spectrometry method was developed for the simultaneous determination of three organophosphorus pesticides, namely, chlorpyrifos, malathion, and diazinon in three different food commodities (milk, apples, and drinking water) employing solid‐phase extraction for sample pretreatment. Pesticide extraction from different sample matrices was carried out on Chromabond C₁₈ cartridges using 3.0 mL of methanol and 3.0 mL of a mixture of dichloromethane/acetonitrile (1:1 v/v) as the eluting solvent. Analysis was carried out by gas chromatography coupled with mass spectrometry using selected‐ion monitoring mode. Good linear relationships were obtained in the range of 0.1–50 μg/L for chlorpyrifos, and 0.05–50 μg/L for both malathion and diazinon pesticides. Good repeatability and recoveries were obtained in the range of 78.54–86.73% for three pesticides under the optimized experimental conditions. The limit of detection ranged from 0.02 to 0.03 μg/L, and the limit of quantification ranged from 0.05 to 0.1 μg/L for all three pesticides. Finally, the developed method was successfully applied for the determination of three targeted pesticides in milk, apples, and drinking water samples each in triplicate. No pesticide was found in apple and milk samples, but chlorpyrifos was found in one drinking water sample below the quantification level.     

Monoclonal-based enzyme-linked immunosorbent assay and immunochromatographic assay for enrofloxacin in biological matrices

Enrofloxacin has been increasingly used in veterinary medicine to treat microbial infections. A simple and reliable analytical method for this drug is required. The current determination by high performance liquid chromatography (HPLC) is sensitive but labor-intensive. This paper reports an enzyme-linked immunosorbent assay (ELISA) using a monoclonal antibody (MAb) and the development of a rapid test kit based on immunochromatography. The detection limits using the ELISA were 10 ppb for chicken liver and muscle, and 1 ppb for cattle milk, respectively. The mean recovery values were 77.3-96.0% for chicken liver, 72.4-92.0% for chicken muscle and 84.0-99.0% for cattle milk. The detection limits using the kit were ca. 100 ppb for chicken muscle and ca. 10 ppb for cattle milk, respectively. All ELISA results for assay of chicken liver, chicken muscle and cattle milk were confirmed using HPLC which is used as the routine assay. The HPLC (x) and ELISA (y) results showed close correlation for chicken liver (y = 8.7 + 0.85x, r2 = 0.99, n = 25), chicken muscle (y = -3.9 + 0.94x, r2 = 0.98, n = 25) and cattle milk (y = 18.4 + 0.92x, r2 = 0.99, n = 25).     

Quantitative determination of dihydrostreptomycin in bovine tissues and milk by liquid chromatography-electrospray ionization-tandem mass spectrometry

Dihydrostreptomycin (DHS) is an aminoglycoside antibiotic used in veterinary medicine in combination with benzylpenicillin for the treatment of bacterial infections in cattle, pigs and sheep. A method to determine its residues in edible tissues of cattle, as well as in milk, was developed and validated. Extraction of DHS from the tissues was performed using a liquid extraction with a 10 mM phosphate buffer containing 2% (w/v) trichloroacetic acid, while milk samples were treated with a 50% (w/v) trichloroacetic acid solution, followed by a solid-phase clean-up procedure on a carboxypropyl (CBA) weak cation exchange column. Ion-pair chromatography, using a mixture of 20 mM pentafluoropropionic acid in water and acetonitrile as the mobile phase, was used to retain DHS and the internal standard streptomycin (STR) on a Nucleosil (5 microm) reversed-phase C18 column. The components were detected and quantified by electrospray ionization (ESI) tandem mass spectrometry. The method could be validated according to EC (European Community) requirements with respect to linearity, trueness and precision, the latter evaluated at the maximum residue limit (MRL) - 1000 ng g(-1) for kidney, 500 ng g(-1) for muscle, liver and fat, and 200 ng g(-1) for milk -, at one-half of the MRL and at one and a half times the MRL. A limit of quantification of 10 ng g(-1) and 1 ng ml(-1) was obtained for all tissues and for milk, respectively, which is far below one-half of the MRL as requested, while the limit of detection was in the low ppb range, varying between 1.9 and 4.2 ng g(-1) for the different tissues tested, and being 0.6 ng ml(-1) for milk. The method was used for the monitoring of DHS residues in incurred tissue and milk samples coming from cattle medicated with DHS in combination with benzylpenicillin by intramuscular injection, in order to evaluate withdrawal times.     

High-performance liquid chromatographic assay of erythromycin from biological matrix using electrochemical or ultraviolet detection

Two chromatographic methods were developed for the determination of erythromycin A (EA) residues in animal tissues (muscle, liver, kidney and fat of cattle, pigs and poultry) and cow's milk. In addition to a more traditional method using electrochemical detection, we developed an original alternative method based on UV detection at 236 nm, by pretreating to create a chromophore in the molecule. An internal standard was used with both methods to check the variability of the analytical system. Analysis times and performance were compared. The recovery of EA from various matrices was greater than 95%. For both methods the quantification limit for EA was 0.25 microgram ml-1 for plasma, 0.025 microgram g-1 for milk and 0.125 microgram g-1 for the other biological matrices. The methods can be used to check for EA residues in these matrices; in fact, the statutory maximum residue limits (MRLs) of EA are 0.4 microgram g-1 in muscle, kidney, liver and fat of beef cattle, sheep, pigs and poultry, and 0.04 microgram g-1 in cow's and sheep's milk.     

Simplified method for the determination of organochlorine pesticides in honey.

A method is described for the detection and quantitative determination of organochlorine pesticides in honey. After extraction with hexane, the pesticides were cleaned-up by adsorption chromatography on a Florisil Sep-Pak cartridge and eluted with 15% diethyl ether in hexane. The detection of organochlorine pesticides was performed by capillary gas chromatography with electron-capture detection. The quantification limit obtained for different pesticides ranged from 0.56 to 2.78 micrograms kg-1 and recoveries from fortified honey samples averaged 89.6%.     

Confirmation of avermectin residues in food matrices with negative-ion atmospheric pressure chemical ionization liquid chromatography/mass spectrometry

A multi-residue LC/MS method has been developed to confirm avermectin drug residues in several food matrices. Ivermectin (IVR), doramectin (DOR), eprinomectin (EPR) and moxidectin (MOX) are confirmed using atmospheric pressure chemical ionization (APCI) with negative ion detection and selected ion monitoring of three to four ions for each compound. The drug residues are extracted from tissue or milk using previously published procedures. IVR and DOR are confirmed at 20 ppb levels in fortified salmon muscle; IVR is also confirmed in tissue from salmon dosed with the drug. Residues of DOR, IVR, and EPR are confirmed in fortified milk at the 20 ppb level and in fortified beef liver at 40 ppb. Residues of MOX can also be confirmed in these matrices, but at slightly higher levels (40-80 ppb).     

Development of an analytical method for penicillin G in bovine milk by liquid chromatography with ultraviolet-visible detection and confirmation by mass spectrometric detection

A liquid chromatographic (LC) method with ultraviolet-visible photodiode array (UV-VIS PDA) detection was developed to measure penicillin G in bovine milk. A liquid chromatographic-mass spectrometric (LC-MS) procedure was divised to confirm the LC method. The method involved diluting milk with a drug-releasing solvent consisting of acetonitrile-methanol-water and ultrafiltration through a 10,000 dalton cutoff filter. Penicillin G was separated from other components in the ultrafiltrate by ion-paired LC using a reversed-phase microbore column eluted with a 25% acetonitrile solution. The LC method was confirmed by thermospray LC-MS. The detection limit for penicillin G determination in milk was estimated to be 10 ppb for LC with UV-VIS PDA and 100 ppb for LC-MS.     

Determination of avoparcin in animal tissues and milk using LC‐ESI‐MS/MS and tandem‐SPE

A highly sensitive and selective method using LC‐ESI‐MS/MS and tandem‐SPE was developed to detect trace amounts of avoparcin (AV) antibiotics in animal tissues and milk. Data acquisition using MS/MS was achieved by applying multiple reaction monitoring of the product ions of [M + 3H]³⁺ and the major product ions of AV‐α and ‐β at m/z 637 → 86/113/130 and m/z 649 → 86/113/130 in ESI(+) mode. The calculated instrumental LODs were 3 ng/mL. The sample preparation was described that the extraction using 5% TFA and the tandem‐SPE with an ion‐exchange (SAX) and InertSep C18‐A cartridge clean‐up enable us to determine AV in samples. Ion suppression was decreased by concentration rates of each sample solution. These SPE concentration levels could be used to detect quantities of 5 ppb (milk), 10 ppb (beef), and 25 ppb (chicken muscle and liver). The matrix matching calibration graphs obtained for both AV‐α (r >0.996) and ‐β (r >0.998) from animal tissues and milk were linear over the calibration ranges. AV recovery from samples was higher than 73.3% and the RSD was less than 12.0% (n = 5).     

Determination of pesticides in aqueous samples by solid-phase microextraction in-line coupled to gas chromatography—mass spectrometry

A multiresidue method was developed for the determination of nitrogen- and phosphorous-containing pesticides (amines, anilides, phosphorothioates, and triazines) by solid-phase microextraction (SPME) in-line coupled to gas chromatography—mass spectrometry (GC/MS). The 85-µm polyacrylate fiber was first dipped into the aqueous sample for a given time and then directly introduced into the heated injector of the gas chromatography—mass spectrometer, where the analytes are thermally desorbed. The method was evaluated with respect to the limit of detection, linearity, and precision. The limit of detection [selected ion monitoring (SIM) mode] depends on the compound and varies from 5 to 90 ng/L. The method is linear over at least 3 orders of magnitude with coefficients of correlation usually ≥0.996. In general, the coefficient of variation (precision) is <10%. The partitioning of the analyte between the aqueous phase and the polymeric phase depends on the hydrophobicity of the compound as expressed by the octanol—water partitioning coefficient P _ow. The addition of sodium chloride has a strong effect on the extraction efficiency. This effect increases with decreasing hydrophobicity (increasing polarity) of the compound. The triazines atrazine, simazine, and terbuthylazine were first identified and quantified in water samples from the effluent of sewage plants by SPME-gas chromatography—nitrogen—phosphorus detection (GC/NPD). For such a complex matrix GC/NPD is not sufficiently selective for an unambiguous identification at low levels (<1 ppb) of pesticides. Selectivity may be enhanced by using SMPE-GC/MS in the SIM mode with three characteristic ions for each pesticide. This method allows an unequivocal identification and quantification at low levels of pesticides in environmental samples. At a target limit of detection below 100 ng/L, SPME-GC/MS represents a very simple, fast, selective, and solvent-free multimethod for the extraction and determination of these nitrogen- and phosphorous-containing pesticides from aqueous samples.     

Validation of a gas chromatography/triple quadrupole mass spectrometry based method for the quantification of pesticides in food commodities

A new multiresidue method has been validated in cucumber matrix for the routine analysis of 130 multiclass pesticide residues by gas chromatography/triple quadrupole mass spectrometry. The pesticides were extracted with ethyl acetate. A first identification of the pesticides was based on a tandem mass spectrometric (MS/MS) screening method, which monitors a single transition for each target compound, in less than 12 min. After that, potentially non-negative samples were analyzed again by the MS/MS confirmation/quantification method, which monitors two or three MS/MS transitions for each compound, also in less than 12 min. Performance characteristics, such as trueness, precision, linear range, detection limit (LOD) and quantification limit (LOQ), for each pesticide were calculated. The average recoveries obtained ranged between 70 and 120% at three different fortification levels (25, 200 and 500 microg/kg) with precision, expressed as relative standard deviation (RSD), values lower than 15%. The calculated LOD and LOQ were typically <3.2 and 9.6 microg/kg, respectively. Such limits were much lower than the maximum residue levels (MRLs) established by European legislation. The proposed methodology was applied to the determination of pesticides in real vegetable samples from Almería (Spain).     

Analysis of 5-vinyl-1,3-oxazolidine-2-thione in complex matrices at ppb level

5-Vinyl-1,3-oxazolidine-2-thione (5-VOT) is a goitrogenic compound released by enzymatic degradation of progoitrin, the most important glucosinolate occurring in rapeseed meal. This paper describes an analytical method for determining the 5-VOT in complex matrices. The method proposed by Quinsac et al. [J. Assoc. Off. Anal. Chem., 75(3) (1992) 529] has been improved by modification of the extraction conditions and the purification steps. The extraction of 5-VOT is performed with hot acid buffer. The first purification step is achieved by solid-phase chromatography (C(18)). The second purification step of 5-VOT is carried out by complexation with phenyl mercury acetate in cyclohexane and, afterwards, by decomplexation using an aqueous solution of sodium thiosulfate. These reactions move 5-VOT from an aqueous to an organic medium, and then back again to the aqueous phase. This procedure ensures a high purification efficiency. The precise quantification of 5-VOT is completed in 12 min by reverse-phase liquid chromatography (C(18)), using an isocratic elution with an ultraviolet detector and with synthetic 4,4-dimethyl-1,3-oxazolidine-2-thione as internal standard. Using this modified method, 5-VOT can be determined in different matrices such as rapeseed meal, animal diets, muscle, several organs (thyroid, liver, kidney and lung) and biological fluids (plasma and milk). The quantification limit of 5-VOT in the sample is of 1 ppb (1 mug kg(-1)), the recovery rate of 5-VOT is about 90% and the repeatability is over 97%.     

Simultaneous determination of multiresidual phenyl acetanilide pesticides in different food commodities by solid‐phase cleanup and gas chromatography‐mass spectrometry

An efficient and sensitive multiresidue method has been developed for quantification and confirmation of 25 phenyl acetanilide pesticides in a wide variety of food commodities including maize, spinach, mushroom, apple, soybean, chestnut, tea, beef, cattle liver, chicken, fish, and milk. Analytes were extracted with acetone–n‐hexane (1:2, v/v) followed by cleanup using SPE. Several types of adsorbents were evaluated. Neutral aluminum and graphitized carbon black cartridge showed good cleanup efficiency. The extract was determined by GC‐MS in the selected ion monitoring mode using one target and two qualitative ions for each analyte. The limits of detection were 0.01 mg/kg for all analytes. The average recoveries ranged from 66.9 to 110.6% (mean 88.8%) and RSDs were in the range 2.0–19% (mean 10.5%) across three fortification levels. The proposed method was successfully applied to real samples in routine analysis and a satisfactory result was obtained.     

A rapid method for the determination of lasalocid in animal tissues and eggs by high performance liquid chromatography with fluorescence detection and confirmation by LC-MS-MS

A simple and rapid method has been developed for the extraction of lasalocid from chicken muscle, eggs and liver and kidney from chicken, pig, sheep and calf. This method allows the screening of a large number of samples, i.e. 30-40 within a working day, and has an overall analysis time of 90 min. Lasalocid standard solution can be detected at 1 ng ml-1 by both HPLC-fluorescence (HPLC-F) and LC-MS-MS; the limit of quantification in fortified samples by the described method is 1 ng g-1. Results show good repeatability and mean 'spiked' recoveries by HPLC-F in the range of 10 to 200 ng g-1 (ppb) of 103, 87, 107, 97, 97, 103, 93, 109 and 100% in chicken muscle, chicken liver, egg, pig liver, pig kidney, sheep liver, sheep kidney, calf liver and calf kidney, respectively. For concentrations between 1 and 6 ng g-1 of spiked lasalocid in eggs and chicken liver by LC-MS-MS, the average recoveries were 76 and 59%, respectively.     

Rapid multiplug filtration cleanup method for the determination of 124 pesticide residues in rice,wheat, and corn

A simple and rapid multiplug filtration cleanup method based on multiwalled carbon nanotubes was developed to determine 124 pesticide residues in rice, wheat, and corn, which could be done in a few seconds without conditioning and elution steps. Various combinations of sorbents were optimized for each matrix with a dispersive solid‐phase extraction procedure to get a satisfactory recovery and clean‐up performance. Good linearity was obtained for all pesticides with calibration curve coefficients larger than 0.9958. Most recoveries for the majority pesticides were between 70 and 120% (n = 5) with relative standard deviations below 20%. The limit of detection was 0.1–1.3 μg/kg, and the limit of quantification was 0.2–4.3 μg/kg for the pesticides in all matrices. The work suggests that the multiplug filtration cleanup method is better than the dispersive solid‐phase extraction method and it could be applied to routinely monitor pesticide residues in market samples.     

Multiresidue pesticides analysis in soils using modified QuEChERS with disposable pipette extraction and dispersive solid‐phase extraction

QuEChERS original method was modified into a new version for pesticides determination in soils. The QuEChERS method is based on liquid–liquid portioning with ACN and was followed by cleanup step using dispersive SPE and disposable pipette tips. Gas chromatographic separation with MS detection was carried out for pesticides quantification. The method was validated using recovery experiments for 36 multiclass pesticides. Mean reco‐veries of pesticides at each of the four spiking levels between 10–300 μg/kg of soil ranged from 70–120% for 26 pesticides with RSD values less than 15%. The method achieved low limit of detection less than 7.6 μg/kg. Matrix effects were observed for 13 pesticides. Matrix effects were compensated by using matrix‐matched calibration. The method was applied successfully using d‐SPE or DPX in the analysis of the pesticides in soils from organic farming and integrated pest management.     

Analytical method development for the determination of four biocides used in antifouling paints in estuarine waters and sediments by gas chromatography-mass spectrometry

Summary Irgarol 1051, chlorothalonil, dichlofluanid and diuron are biocides utilised in antifouling paints as alternatives to organotin compounds, after restrictions imposed in the use of tributyltin in 1987. Effective analytical methods for the simultaneous determination of these four biocides in waters and sediments have been developed and method performance data are presented. Quantification is by gas chromatography—electron ionisation mass spectrometry (GC-EI-MS). The method involves the simultaneous extraction of the biocides from water with dichloromethane or from sediments with dichloromethane and acetone. For the determination of diuron the extract was methylated prior to GC analysis to avoid thermal degradation in the instrument. The method was applied to water and sediment samples spiked with the biocides. The highest detection sensitivities were achieved in the selected-ion monitoring (SIM) mode. Recovery studies were performed at 20, 2 and 1 ppb for all biocides in water and 400, 40 and 20 ppb in sediments. The percentage recoveries ranged between 90 and 100% for waters and 80 and 90% for sediments. Seven determinations were made at each concentration level along with a procedural blank. The quantification limit of the method was around 0.2 ppb for water and 5 ppb for sediments depending on the individual compound.     

Determination of pyrimethamine in animal tissue and egg by liquid chromatography with fluorescence detection

A sensitive and selective liquid chromatographic (LC) assay was developed to determine the concentration of pyrimethamine in animal tissue and egg by fluorescent derivative. Animal samples were extracted with acetonitrile, centrifuged, and purified by hexane. Fluorescent derivatization was performed by reacting pyrimethamine with chloroacetaldehyde and subjected to LC with fluorescence detection (excitation wavelength 300 nm, emission wavelength 420 nm). The limit of detection was 10 ng/g (10 ppb) and the standard calibration curve was linear in the range of 1-100 ppb (0.01-1 ng/10 microL). Recoveries from samples fortified at levels of 0.1 and 1 ppm (microg/g) were 61.0-77.4 and 65.5-81.2%, respectively. The method was applied to the monitoring of marketed samples. Pyrimethamine was not determined in any of the 70 samples: 20 swine muscle; 20 chicken muscle; 10 chicken liver; and 20 egg.     

Method validation for the determination of lead in raw cow's milk by electrothermal atomic absorption spectrometry

In this study, lead in raw cow's milk has been determined by validated electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. Maximum pyrolysis and optimum atomization temperatures of lead were determined in the presence of modifiers. Pd + Mg(NO3)2 has been found a powerful modifier mixture for the determination of lead. The analytical parameters of the method such as limit of detection, limit of quantification and the effect of interfering ions have been investigated. The detection limit (3sigma) achieved by the method was calculated to be 0.62 ng/mL for Pb. Repeatability of the method evaluated as the relative standard deviation of 16-17 replicates using 5 ng/mL, under optimum experimental conditions were about 1.5% for synthetic sample solution and about 3% for real sample (N = 5). The described method has been validated by analyzing certified reference material (BCR-CRM 150) and by comparing the results with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The validated method was applied to raw cow's milk samples produced in 7 different regions of Turkey in 2003-2004. Raw cow's milk contained a mean (range) of 31.4 (2.5 - 313) microg kg(-1) lead with a relative error below 2%.     

Analysis of Phosmet and Azinphos-Methyl in Apples by High-Performance Liquid Chromatography

Abstract

A high-performance liquid chromatography (HPLC) method has been developed to analyze two organophosphate insecticides (phosmet and azinphosmethyl) in apples. The procedure includes a novel extraction whereby whole apples are sonicated for 2 min in 100 ml of MeOH to remove the pesticides. Reversed-phase HPLC separation was accomplished with an Ultremex C18 column and acetonitrile:methanol:water as the eluent. Detection was at 224 nm for phosmet and 300 nm for azinphos-methyl. For both pesticides the limit of detection was 0.5 ppb and the linearity was from 1 to 405 ng injected. Average recoveries were 80% for phosmet and 86% for azinphos-methyl. Thirteen apple varieties comprising 240 apples were analyzed from supermarkets and roadside stands for phosmet (amount found ranged from none detected to 1233 ppb) and azinphos-methyl (amount found ranged from none detected to 388 ppb). Confirmation of phosmet and azinphos-methyl was made by UV spectral scans.     

Rapid determination of chlorinated pesticides in fish by freezing-lipid filtration, solid-phase extraction and gas chromatography-mass spectrometry

An analytical method has been developed for measuring 24 chlorinated pesticides in fish tissue samples. Extraction of chlorinated pesticides was carried out by ultrasonication using an acetone-n-hexane (5:2, v/v) mixture. Most of the lipids in the extract were eliminated by freezing-lipid filtration, prior to solid-phase extraction (SPE) cleanup. During freezing-lipid filtration, about 90% of the lipids extracted from the fish samples were easily removed without any significant losses of chlorinated pesticides. For purification, SPE using Florisil was shown to be more effective than silica. Quantification was performed using gas chromatography-mass spectrometry in the selected ion monitoring mode. Spiking experiments were carried out to determine the recovery, precision, and limits of detection (LODs) of the method. The overall recovery was above 80% in the spiked fish tissue sample at 100 ng/g level. The detection limits for chlorinated pesticides were ranged from 0.5 to 5 ppb, except for endosulfan I and II which was 20 ppb. The newly developed method is demonstrated to give efficient recoveries and LODs for detecting chlorinated pesticides spiked into fish tissue with high lipid content.